.\" $OpenBSD: PKCS7_sign_add_signer.3,v 1.13 2020/06/10 11:43:08 schwarze Exp $
.\" full merge up to: OpenSSL df75c2bf Dec 9 01:02:36 2018 +0100
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.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
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.Dd $Mdocdate: June 10 2020 $
.Dt PKCS7_SIGN_ADD_SIGNER 3
.Os
.Sh NAME
.Nm PKCS7_sign_add_signer
.Nd add a signer to a SignedData structure
.Sh SYNOPSIS
.In openssl/pkcs7.h
.Ft PKCS7_SIGNER_INFO *
.Fo PKCS7_sign_add_signer
.Fa "PKCS7 *p7"
.Fa "X509 *signcert"
.Fa "EVP_PKEY *pkey"
.Fa "const EVP_MD *md"
.Fa "int flags"
.Fc
.Sh DESCRIPTION
.Fn PKCS7_sign_add_signer
adds a signer with certificate
.Fa signcert
and private key
.Fa pkey
using message digest
.Fa md
to a
.Vt PKCS7
signed data structure
.Fa p7 .
.Pp
The
.Vt PKCS7
structure should be obtained from an initial call to
.Xr PKCS7_sign 3
with the flag
.Dv PKCS7_PARTIAL
set or, in the case or re-signing, a valid
.Vt PKCS7
signed data structure.
.Pp
If the
.Fa md
parameter is
.Dv NULL ,
then the default digest for the public key algorithm will be used.
.Pp
Unless the
.Dv PKCS7_REUSE_DIGEST
flag is set, the returned
.Dv PKCS7
structure is not complete and must be
finalized either by streaming (if applicable) or by a call to
.Xr PKCS7_final 3 .
.Pp
The main purpose of this function is to provide finer control over a
PKCS#7 signed data structure where the simpler
.Xr PKCS7_sign 3
function defaults are not appropriate, for example if multiple
signers or non default digest algorithms are needed.
.Pp
Any of the following flags (OR'ed together) can be passed in the
.Fa flags
parameter.
.Pp
If
.Dv PKCS7_REUSE_DIGEST
is set, then an attempt is made to copy the content digest value from the
.Vt PKCS7
structure: to add a signer to an existing structure.
An error occurs if a matching digest value cannot be found to copy.
The returned
.Vt PKCS7
structure will be valid and finalized when this flag is set.
.Pp
If
.Dv PKCS7_PARTIAL
is set in addition to
.Dv PKCS7_REUSE_DIGEST ,
then the
.Dv PKCS7_SIGNER_INO
structure will not be finalized, so additional attributes can be added.
In this case an explicit call to
.Fn PKCS7_SIGNER_INFO_sign
is needed to finalize it.
.Pp
If
.Dv PKCS7_NOCERTS
is set, the signer's certificate will not be included in the
.Vt PKCS7
structure, though the signer's certificate must still be supplied in the
.Fa signcert
parameter.
This can reduce the size of the signature if the signers certificate can
be obtained by other means: for example a previously signed message.
.Pp
The signedData structure includes several PKCS#7 authenticatedAttributes
including the signing time, the PKCS#7 content type and the supported
list of ciphers in an SMIMECapabilities attribute.
If
.Dv PKCS7_NOATTR
is set, then no authenticatedAttributes will be used.
If
.Dv PKCS7_NOSMIMECAP
is set, then just the SMIMECapabilities are omitted.
.Pp
If present, the SMIMECapabilities attribute indicates support for the
following algorithms: triple DES, 128-bit RC2, 64-bit RC2, DES
and 40-bit RC2.
If any of these algorithms is disabled, then it will not be included.
.Pp
.Fn PKCS7_sign_add_signer
returns an internal pointer to the
.Vt PKCS7_SIGNER_INFO
structure just added, which can be used to set additional attributes
with the functions described in
.Xr PKCS7_add_attribute 3
before it is finalized.
.Sh RETURN VALUES
.Fn PKCS7_sign_add_signer
returns an internal pointer to the
.Vt PKCS7_SIGNER_INFO
structure just added or
.Dv NULL
if an error occurs.
In some cases of failure, the reason can be determined with
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr EVP_DigestInit 3 ,
.Xr PKCS7_add_attribute 3 ,
.Xr PKCS7_final 3 ,
.Xr PKCS7_get_signer_info 3 ,
.Xr PKCS7_new 3 ,
.Xr PKCS7_sign 3
.Sh HISTORY
.Fn PKCS7_sign_add_signer
first appeared in OpenSSL 1.0.0 and has been available since
.Ox 4.9 .
